New to me A25C

[SlatcoAu]

Picked up a 1997 A25C SN 5350V9574 at auction and it seems to have the typical age related issues. Just got it to my yard today, drove it around for a bit, and it upshifts/down shifts through forward gears but when backing up if you are fwd-reversing a couple times eventually it will not engage reverse. Shut it off/start it up again and away we go. Issues along with associated questions/assumptions below:

1. The brake hydraulic light is on. My research has led me to believe that one of the stroke indicators is tripped? Are these switches normally open/normally closed or is the system expecting to see a certain resistance range? Also could this be affecting the engaging of the reverse gear?
2. While driving around should I expect a difference in reading between the transmission in/out speeds on the Contronic display? If so what is typical?
3. The engine idles really low at 500rpm. I went to adjust the low idle screw but it is already maxed out. I presume there is a adjustment internal to the Bosch pump that needs to be done?
4. I read that the diff lock is active when the park brake is on. My 6x6 diff lock light is on when the park brake is applied but goes off when disengaged and driving- is this proper?

Thanks in advance for any guidance anyone provides!

 

[sfrs4]

Hi SlatcoAU
When you are going from forward to reverse and vise versa, are you coming to a complete stop? the ECU won't let you select a gear if you are still moving.
1. The stroke sensors are a simple on/off affair and should not effect the gear changing
2. There should be a slight difference between input and output speeds, i can't remember what exactly
3. Engine idle should be 650-700, Check the throttle linkage, if its worn it might not be coming back to the stop correctly and also could be effecting the load sensor reading which in turn could be effecting you gear selecting
4. Yes the diff is activated when the park brake is applied and disengaged when driving.

 

[SlatcoAu]

Thanks Sfrs4. I will make sure I am at a complete stop before gear changes.
1. Thanks for the info on the stroke sensors, as per your response they have no effect on operation other than illuminating the brake hydraulics light? Yes, I need to determine why they overstroked.
2. Ok, noted.
3. Hmmm, this needs further investigation. Any other "interlock" that could be causing the shift hesitancy. I am dreading that it may be the worst case scenario of the trans and am hesitant to think that at this time as when it is in gear it is really strong.
4. The fuel level gauge is "Not Functioning Correctly" and I can see that the gauge in the dash is newer which would point me towards the sending unit. I read on a previous thread of installing a aftermarket VDO sending unit but was curious if Volvo still carried the one that came with the truck.

 

[sfrs4]

Hello Slat
1. Yes the only thing the stroke sensor does is illuminate the light, probably either air chamber failed or pads just getting really low
3. Take a look at where the throttle cable attaches to the pump through a fork. this fork linkage wears, and the springs start to get tired, also be aware the link from there to the load sensor has left and right handed thread on it
4. As far as i am concerned Volvo no longer stocks the gauge in the cab, happy to told i'm wrong though.

 

[SlatcoAu]

Thanks Sfrs4. As I spend more time with this truck I am figuring out the little things. The load sensor looks to be recently changed as does the linkage. I suspect there is still some issues there though with the really low idle. I will get the idle fixed and do the load sensor calibration.

Next question for me is how does the ECU communicate with the transmission? Is it CANbus? I noticed when I had my issues with trans not going into gear the Contronic would display "Trans Comm Error". Also I believe the Contronic gets it data from the ECU? Once I shut the truck down and restarted, the trans started communicating again and away we go.

 

[sfrs4]

The ECU and the transmission are hard wired, no Can bus until the D series (plastic) trucks, from memory the Ecu- transmission loom exits at the back of the truck and makes a very tight turn under the cab, where this turn is is prone to rubbing through the wires, maybe check the loom and pin's could be some age related corrosion, some electrical contact cleaner sprayed into the plugs wouldn't go amiss, there is a whole procedure for setting and adjusting the idle speed, but one of the fitters here has just said if its already adjusted to the max and the linkage looks good, "it's more than likely the rack in the fuel pump is worn and the pump is on it's way out"

 

[SlatcoAu]

THanks again. Will report back later after I have had some time to work on things.

 

[Dave Neubert]

I had one do a similar thing had to replace the shifter control

 

[SlatcoAu]

Ok fellas, I feel like I am on a path forward. Take a look at the Contronic display Turbo In speed and Output speed. I pulled my sensor for output speed and it appears it is 26 yrs old and possible damaged? I have a new one ordered but do you guys think I am on the right track? Or am I delusional and my transmission is really slipping that bad ?

 

[SlatcoAu]

Ok, it was not this sensor. The difference is a result of what gear the transmission is in. This sensor was on the drop box. Next issue is transmission does not seem to shift down but rather when stopping it coasts down to neutral and then will not re engage the gear without turning the truck off. I have the Volvo dealer mechanic next week coming to take a look. Thanks for all the help up to this point.

 

[SlatcoAu]

Ok Volvo mechanic came a couple times. Swapped ECU and got error message pertaining to input speed sensor. Waiting for new speed sensor and will try that. I am really hoping that is it.

 

[SlatcoAu]

Well after waiting for ever for Volvo dealer, I took matters into my own hands and ordered a new input speed sensor from Centranz. Great prompt service and I had it 4 days after ordering which is excellent for a international order. Meanwhile I got a call from Volvo dealer telling me they would have to pull the transmission to access the speed sensor as it was behind the torque convertor. I said sorry man, the repair manual I have says it is under the sump and I will do it myself. (I shudder to think if I had not done my due dilligence and sent my truck there for them to pull the transmission for no reason.) Anyways, I dropped the pan this evening to change out the speed sensor. First discovery- suction screen plugged with non metallic material- perhaps this is a from a hose that was/is rotting? Or is this clutch pack material (not sure what the clutches are made of in this thing). After dropping the pan there was a bunch of material in there as well.

 

[SlatcoAu]

As I looked closer, it also appears that I have a couple broken wires but I am hoping someone can confirm that those should actually terminate somewhere. I am by myself otherwise I would meter them back to the ECU and see what they are. I

 

[SlatcoAu]

Dropped the control unit to see what was up. Broken grounds, loose grounds, broken support brackets and some wiring that appears to have rubbed through the insulation in several spots.

 

[SlatcoAu]

Will be ordering a new harness to replace this one. Stay tuned!

 

[chickenminer]

Oh man .... what a mess in there! Glad you're getting it figured out though.

 

[sfrs4]

That looks like friction material, that amount means not good news unfortunately, the wiring loom may be a good idea as Volvo only has 4 left via my contact. ZF may have some, as its there box, but its hard work talking to zf direct somedays.

 

[SlatcoAu]

Yes, unfortunately my transmissions days are numbered. I have fixed up the old harness and cleaned everything up. I am going to reinstall and hope that I can at least get 50-100hrs out of it before I have to replace/rebuild. In other news all my other repairs went well lol (wheel seal - it did have the updated spacer, fuel gauge and idle adjustment) For the idle I looked closer and the nut that is used to tension the idle screw was on the wrong side of the mounting plate, once I moved it to the proper side I had the correct adjustment. Thanks again everyone for the help and assistance.

 

[Oros]

Got Volvo a25c some guy replaced wiring basic need transmission info to repair the mess no gearshift on truck

 

[sfrs4]

Got Volvo a25c some guy replaced wiring basic need transmission info to repair the mess no gearshift on truck

sorry to sound rude, but could you try explaining that a little clearer?
I roughly guess you have a new to you truck that has had some " temporary" work done. what do you actually have and not have and what is wrong exactly.
At least you got the most important bit the machine and serial number.